This invention relates generally to a system for storing a quantity of continuous strip material such as tape or film. More particularly, the invention describes a method and apparatus for continuously storing motion picture film on edge on a flat rotating platter, as part of an endless loop projection system.
It has long been recognized in motion picture projection that an endless loop system is desirable, in order to eliminate the need for manual rewinding and rethreading of film in repeated renditions of a program. A number of attempts have been made to provide for storing the film in a coil on a rotating turntable or platter in such a way as to minimize relative longitudinal movement between adjacent film layers in the coil, and yet permit, during each platter revolution, a predetermined length of film to be withdrawn from the center of the coil while the identical length of film is being added to the outside of the coil. The prior systems produce a series of angularly spaced, inwardly directed rounded cusps in the film coil, and are exemplified by the two U.S. Pat. Nos. to Johnson, 4,066,221 and 4,186,891 and the U.S. Pat. No. 4,208,018 to Wilkinson. These patents, in common with other prior systems known to the present inventor, include an application apparatus for incoming film which feeds or applies the incoming film to the rotating platter at a constant linear speed. Separate means are provided in these systems for shaping the film in the coil into a number of spaced inwardly directed cusps.
The present invention distinguishes over the prior systems just mentioned by providing a method and apparatus in which incremental lengths of the incoming film are accurately metered onto the rotating coil at selected sectors of the platter at a varying linear rate per degree of platter rotation whereby an exact equal length of film is applied for every complete revolution of the platter. The method and apparatus of the present invention applies incoming film during one complete turn of the platter at a selected linear rate for a sector of the platter, then at a diminishing linear rate down to a minimum linear rate, then at an increasing linear rate back to the selected linear rate. As will be seen in the application of film to one of the sectors, a constant selected linear rate forms arcuate sections while in the application of film to the portions of varying and lowered linear rates a straight section of film is formed, substantially in the shape of a chord of a circle. An arcuate section and an adjacent straight section are referred to as a "cycle." The straight sections or chords automatically form themselves into cusps as successive film layers are applied in chord shape. In the illustrative form of the invention disclosed herein, the cycle above described is repeated three times during each revolution of the platter. The varying speeds or linear rates of film application are achieved by a specially shaped platter geared cam track formed with arcuate sections alternating with chord sections corresponding in angular relation with respect to the axis of rotation as the arcuate and chord sections formed by the application of film to the platter margin. The film is applied by an application arm having a geared cam follower cooperating with the platter geared cam track.
Formation of the inwardly directed cusps may be facilitated by providing, in the sectors including the chord sections, skid means in the form of skid strips of material having a low coefficient of friction, the strips extending generally radially of the platter within the segments mentioned. The strips may be made, for example, of polytetrafluroethylene (sold under the registered trademark "Teflon") or other material presenting an upper surface of substantially lower friction than the platter itself, to to allow freedom of inward movement of the film as it is being formed into cusps. The shapes of the arcuate portions of the coiled film may desirably be preserved by flat anchor pads of rubber or equivalent material having a comparatively high coefficient of friction. These pads thus serve as anchors to assist in retaining the arcuate portions of the film coil is between the arcuate sections and also to hold the outermost chord sections of the film coil under a taut tensioned condition.
Template means may be provided to assist in maintaining the shape of the arcuate portions of the film coil, during initial loading or make-up of the film coil on the platter. Each template means desirably includes a central template block and a pair of laterally spaced smaller wing blocks, the three blocks being joined by a flexible strip having a width similar to that of the film, to form a template set. The template sets may be left in place during complete loading of the turntable, and then removed when loading is completed and the endless loop is formed.
It is therefore the principal object of the present invention to disclose a novel system for storing film in a coil on a rotating platter. Additional objects are to disclose such a system for use in an endless loop projection system and using a geared camming relationship to accurately control the rate of film application to the coil; to accurately apply and withdraw equal lengths of film to and from the storage platter during each revolution of the storage platter; to disclose method and apparatus for preliminary shaping of the film coil during initial stages of loading or make-up of the film coil; and for other and additional objects as will be understood from a study of the following illustrative form of the invention, taken in connection with the accompanying drawings.